make 'respect_downstream_limits' configurable

Submitted by Marco Munderloh

Assigned to Intel GFX Bugs mailing list

Link to original bug (#111516)

Description

Created attachment 145203
The boolean should be configurable as a module option

In our company, we have a lot of Dell U2713HM in use. We recently switch from nvida to onboard intel graphics for all our computers and now have the problem that these old monitors only support their full resolution (2560x1440) on Dual-Link DVI or DP. On our mainboards, only the HDMI output is available. On HDMI, the monitor only supports 1920x1080.

However, if the port_clock is increased beyond limits, the 2560x1440 mode works perfectly fine with this monitor. I used the monitor for years this way, until it suddenly did not work anymore because the respect_port_limits was included to intel_hdmi.c as a bug fix - which broke it for me.

I understand that the problem is the monitor firwmare, but I am patching my kernel for years now whithout problems (I'm uisng the intel graphics since we bought the monitors) and I always hoped that the fixed boolean will once become a configurable module parameter - which never happend.

So I'm asking if it would be possible to make the fixed boolean a module parameter (like respect_port_clock_limit or so). I'm not good at kernel programming so I don't really know how to do this, but I provided a patch where the boolean needs to be placed.

Patch 145203, "The boolean should be configurable as a module option":
intel_hdmi_port_clock.patch